Determining the gravitational distortion of an antenna under test

The paper serves to demonstrate the extremely close correlation of the gravitational distortion measured as a by-product of a series of RF range tests and the distortion predicted during the design stage by the standard engineering program, NASTRAN. The antenna under test (AUT) was a slotted waveguide array, 1.9×1.5 m built on a tubular steel space-frame. The 32 radiating waveguides were fed by a fixed 1:32 waveguide power divider, three sets of replaceable shims were used to provide three different beam shapes. Additionally, there were three different configurations of radiating waveguide used for the tests. Thus there were effectively nine AUTs; three waveguide sets each with three beams. In the test range, the pointing of the AUT in test range coordinates was measured by the range theodolite using four targets set at each corner of the antenna. Fine lines on the targets were set to be in a plane parallel to the best fit (least squares) plane through the radiating surface